LP3952 Datasheet, PDF (30/46 Pages) National Semiconductor (TI) – 6-Channel Color LED Driver with Audio Synchronization

LP3952
SNVS518A – JULY 2007 – REVISED MARCH 2013
Symbol
C_VREF
C_VDDIO
R_RBG
R_RT
D₁
C_ASE
LEDs
Symbol explanation
C between V_REF and GND
C between V_DDIO and GND
R between I_RGB and GND
R between I_RT and GND
Rectifying Diode (Vf @ maxload)
C between Audio input and ASE
Application Examples
EXAMPLE 1
Value
100
100
5.6
82
0.3
100
Unit
Type
nF
Ceramic, X7R
nF
Ceramic, X7R
kΩ
±1%
kΩ
±1%
V
Schottky diode
nF
Ceramic, X7R / X5R
User defined
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There may be cases where the audio input signal going into the LP3952 is too weak for audio synchronization. This
figure presents a single-supply inverting amplifier connected to the ASE input for audio signal amplification. The
amplification is +20 dB, which is well enough for 20 mVp-p audio signal. Because the amplifier (LMV321) is operating
in single supply voltage, a voltage divider using R3 and R4 is implemented to bias the amplifier so the input signal is
within the input common-mode voltage range of the amplifier. The capacitor C1 is placed between the inverting input
and resistor R1 to block the DC signal going into the audio signal source. The values of R1 and C1 affect the cutoff
frequency, fc = 1/(2π*R1*C1), in this case it is around 160 Hz. As a result, the LMV321 output signal is centered
around mid-supply, that is V_DDA/2. The output can swing to both rails, maximizing the signal-to-noise ratio in a low
voltage system
30
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